bug#11339: 24.1.50; read-{buffer,file-name}-completion-ignore-case fails on non-ascii

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: stephen.berman@gmx.net,  11339@debbugs.gnu.org,  stefan@marxist.se
> Date: Fri, 08 Nov 2019 17:36:08 -0500
> 
> > The patch below fixes Stefan's simplified test case, but the original
> > problem is still unsolved: "C-x b ba TAB TAB" says "Sole completion".
> >
> > What did I miss?
> 
> It still fails when you swap the two elements in the list :-(
> I don't have time to dig into the code now, tho,

What about the below?  It passes all the tests, and also fixes the
original use case.

diff --git a/src/minibuf.c b/src/minibuf.c
index f6cf47f..1e87c50 100644
--- a/src/minibuf.c
+++ b/src/minibuf.c
@@ -1323,13 +1323,13 @@ DEFUN ("try-completion", Ftry_completion, 
Stry_completion, 2, 3, 0,
          else
            {
              compare = min (bestmatchsize, SCHARS (eltstring));
-             tem = Fcompare_strings (bestmatch, zero,
-                                     make_fixnum (compare),
-                                     eltstring, zero,
-                                     make_fixnum (compare),
+             Lisp_Object lcompare = make_fixnum (compare);
+             tem = Fcompare_strings (bestmatch, zero, lcompare,
+                                     eltstring, zero, lcompare,
                                      completion_ignore_case ? Qt : Qnil);
              matchsize = EQ (tem, Qt) ? compare : eabs (XFIXNUM (tem)) - 1;
 
+             Lisp_Object old_bestmatch = bestmatch;
              if (completion_ignore_case)
                {
                  /* If this is an exact match except for case,
@@ -1363,7 +1363,12 @@ DEFUN ("try-completion", Ftry_completion, 
Stry_completion, 2, 3, 0,
                    bestmatch = eltstring;
                }
              if (bestmatchsize != SCHARS (eltstring)
-                 || bestmatchsize != matchsize)
+                 || bestmatchsize != matchsize
+                 || (completion_ignore_case
+                     && !EQ (Fcompare_strings (old_bestmatch, zero, lcompare,
+                                               eltstring, zero, lcompare,
+                                               Qnil),
+                             Qt)))
                /* Don't count the same string multiple times.  */
                matchcount += matchcount <= 1;
              bestmatchsize = matchsize;